1. Field of the Invention
This invention relates to a vertical heat treating apparatus used in a thermal diffusion process or a film formation process in manufacturing semiconductor devices.
2. Description of the Related Art
Recently, there has been used vertical heat treating apparatuses which can be located in a small space and can be operated in a dustless state.
The vertical heat treating apparatus of this type is provided in a casing with a reaction tube, a uniformly heating tube surrounding the reaction tube, a heater and a substantially vertical heat treating furnace made of heat insulating material or the like. In the lower portion of the casing is provided a boat elevator for loading a wafer boat, which holds semiconductor wafers (which are articles to be processed), in and unloading the wafer boat from the heat treating furnace. An opening through which the semiconductor wafers are loaded in and unloaded from the heat treating furnace is formed in the front face of the casing in which the heat treating furnace and the boat elevator are housed.
Vertical heat treating apparatuses have been known which each have an air fan and a dust filter provided in the rear lower portion of the casing such that clean air is caused to flow from the rear portion to the front portion in the region of the boat elevator thereby to prevent the attachment of dust to the wafers.
The floor space can be rendered less in these vertical heat treating apparatuses than in the horizontal heat treating apparatuses in which a heat treating furnace is disposed substantially horizontally. Further, in the vertical heat treating apparatus, a wafer boat is loaded in and unloaded from the heat treating furnace without contacting the wafer boat with the reaction tube, allowing for dustless heat treating in the apparatus.
There have been used semiconductor wafers having a large diameter such as 8 inches, and the circuit patterns of semiconductor devices have become finer and finer. In order to accord with this tendency, it is required in the vertical heat treating apparatus that wafers having a large diameter be processed by elevating the yield of the processed wafers so as to prevent dust from attaching to the wafers, the floor space be reduced